There are many situations in which a mobile device user is not able to get a global positioning system (GPS) signal to determine his or her precise location. This may be due to interference, or because of poor exposure to the GPS satellites (e.g., due to the terrain or environment, such as because of trees or buildings, or when underwater or underground). Moreover, not all mobile devices have GPS capabilities.
One solution to determine a global position without adequate GPS signals is assisted GPS. Assisted GPS relies on Wi-Fi network communication with an assisting server. Another solution that attempts to determine a global position without GPS at all is to use triangulation and multilateration based upon cellular towers, which rely on the presence of cell towers that are able to communicate with the device. However, these resources are not always available, and even when available, these alternative solutions often do not tend to work particularly well.